Topotactic Ion Exchange in a Three-Dimensional Close-Packed Trirutile Structure with an Octahedral Network

Abstract

Topotactic ion exchange in open-framework solids and oxides with layered and tunnel structures has resulted in the formation of a variety of metastable functional materials that are inaccessible otherwise. These ion exchanges are primarily limited to the above structure types because of the presence of labile ions as loosely held charge-compensating cations/anions as in the framework or tunnel structures or the lability of the ions/charged motifs in interlayer galleries of layered oxides. While such topotactic exchanges are common in the above structure types, they are rare in the three-dimensional (3D) close-packed structures based solely on corner- and/or edge-connected polyhedral networks. Herein, we demonstrate divalent iron exchange in a close-packed all-octahedral-coordinated trirutile oxide. This has enabled the transformation of a near-ultraviolet-absorbing diamagnetic insulating oxide into a visible-light-active paramagnetic semiconductor. An ion exchange of this kind may open up avenues for the development of metastable functional oxides with a variety of other 3D structures and diverse properties.

Renaissance of Topotactic Ion‐Exchange for Functional Solids with Close Packed Structures

“…The exchangeable Li cations are coordinated within its octahedral sites. For large, micrometer‐sized particles, a nearly complete cation exchange with Fe(II) cations in a 0.2 M aqueous solution occurs at only 333 K of up to ∼90‐92 %, or Li 1‐ x Fe x /2 MWO 6 ( x =0.9 to 0.92; 2 : 1 ratio of Li : Fe) [26,27] . The ‘MWO 6 ’ networks, having buckled close‐packed layers, are preserved with the incorporation of Fe(II) cations over 25 % of the octahedral sites.…”

“…For large, micrometer-sized particles, a nearly complete cation exchange with Fe(II) cations in a 0.2 M aqueous solution occurs at only 333 K of up to ~90-92 %, or Li 1-x Fe x/2 MWO 6 (x = 0.9 to 0.92; 2 : 1 ratio of Li : Fe). [26,27] The 'MWO 6 ' networks, having buckled closepacked layers, are preserved with the incorporation of Fe(II) cations over 25 % of the octahedral sites. The thermodynamic driving force of the reaction has yet to be explored, as both solids are metastable.…”

Metastable γ-Li2TiTeO6: Negative Chemical Pressure Interception and Polymorph Tuning of SHG

“…8,21,22 (b) Topotactic ion exchange is a chemical approach that replaces cations, anions, or ionic groups with new ones under relatively mild conditions, without breaking the original structure frameworks. This approach is T h i s c o n t e n t i s 24 the only two reported topotactic products from three-dimensional (3D) close-packed precursors. 3D and quasi-2D perovskite derivatives, such as the Ruddlesden− Popper, Dion−Jacobson, and Aurivillius type phases, could transform into one another by manipulating ion-exchange reactions.…”

Tri-α-PbO2-Type Fe–Sb Tungstate by Topotactic Ion Exchange of LiSbWO6

“…The Li exchange by Fe(II) has allowed the transformation of a near-ultraviolet-absorbing diamagnetic insulating oxide into a visible-light-active paramagnetic semiconductor. 31 The analogous composition, LiSbWO 6 , attainable by replacing Nb of trirutile LiNbWO 6 with a p-block element like Sb does not stabilize in the same structure. Initially, LiSbWO 6 was reported by Blasse and de Pauw with an ordered columbite structure.…”

“…The structure is made up of an all edge- and corner-connected octahedral network, where the Li ions occupy part of the octahedral network of the rutile structure in a quasi-ordered fashion. The Li exchange by Fe­(II) has allowed the transformation of a near-ultraviolet-absorbing diamagnetic insulating oxide into a visible-light-active paramagnetic semiconductor …”